Duplex copying, i.e., copying image information to both sides of a single sheet of paper, is an important feature in copying machines. Duplex copying is desirable because it reduces the amount of paper required in copying in comparison to simplex (single side) copying, produces attractive copy sets, and can simulate the appearance of a printed book. Generally, such copying is accomplished in either one of two methods. In a first method, first side copies are produced in a reproduction processor and stacked in a duplex tray. When a set of first side copies is complete, the copies are fed out of the duplex tray and returned to the reproduction processor with an odd number of inversions in the total duplex path to receive second side image information, and subsequently passed to an output. Alternatively, first side copies may each be returned directly to the reproduction processor to receive second side copies thereon, without stacking, for example, as described in U.S. patent application Ser. No. 814,827. This type of copying finds particular use with respect to copying two documents placed on a platen for sequential copying, sometimes referred to as two-up copying.
Book style duplex copying, as used herein and with reference to FIG. 1 (a) refers to the production of duplex copy sets which are suitable for reading as a book, from top to bottom from the same sheet edge, with the image top portion on both sides of the sheet adjacent the top edge of the sheet, for binding along a side edge with respect to the image. This appearance is generally only achieved in present duplex-capable reproduction machines, however, when copy sheets are fed through the reproduction processor to receive image information on one or both sides of the copy sheet with the image top to bottom alignment or orientation, as the image is normally viewed, oriented on the sheet transverse to the direction of sheet feeding. When duplex copies are made with image top to bottom alignment oriented on the sheet in the direction of sheet travel in the same reproduction machines, the resulting two-sided copies do not have the top portions of the image along a common edge of the sheet. Instead, the image top portions are adjacent opposed edges on each side of the sheet, which, when the copy set is bound along a side edge in a book style format, provides the second sides of the sheets upside down with respect to the first sides of the sheets. This type of copying, illustrated at FIG. 1(b), sometimes called military style duplex, and hereinafter referred to as pad style duplex, provides easy viewing only if the copy set is bound along the top edge and read by turning pages upwardly to read the back side of each sheet. While pad style duplex copying has certain applications, it is frequently undesirable in duplex copying usage.
Heretofore, in duplex capable copying machines where it has been desirable to provide book style duplex copying from simplex originals, it has been necessary for the machine to provide a paper path and processor accommodating LEF (long edge first) sheets and place images on the sheet having a top to bottom alignment oriented transverse to the direction of sheet travel. This arrangement adds significantly to the cost of the machine, as it requires paper path and processing elements to accommodate the long edge of sheets fed through the machine. In very low cost machines, it is desirable to provide only a narrow processor, accommodating for example, 81/2.times.11 inch sheets fed SEF (short edge first). The width of the paper path and processing elements in such a machine are only required to accommodate the 81/2 inch length of the sheet, as opposed to machines required to accommodate at least 11 inch widths to accommodate the long edge of a 81/2.times.11 inch sheets. However, this arrangement ordinarily precludes the desirable book style duplex from simplex documents, as the bulk of simplex documents copied have images oriented with the image top portion adjacent a short edge of the document sheet. Alternatively, an operator desiring to produce duplex copies from simplex documents on SEF sheets, must manually rotate every other document to be copied by 180.degree. prior to copying. This is inconvenient, and potentially confusing, allowing the possibility of operator errors. Additionally, such an arrangement precludes the simple use of automatic document feeders to feed the set of documents to be copied past the platen, as an operator seeking to take advantage of the increased speed in automatic document handling must manually prepare the set of simplex documents to be copied with every other sheet rotated with respect to the previous sheet, and re-order the document set subsequent to copying. Of course, this is not merely a problem of small copiers, since this characteristic is present in all copiers where SEF and duplex copying from simplex originals are provided. For example, for copiers with an 11 inch wide paper path, for simplex to duplex copying, 81/2.times.11 inch copies are produced book style, because the sheets are fed LEF, but legal size copies 81/2.times.14 inch) are fed SEF, and so produce pad style duplex copies. Large copies, such as 11.times.17 inch sheets are commonly fed with the short edge first, and depending on image orientation, also experience the problem. Likewise, for ledger or landscape format copies where images are arranged to have a top to bottom alignment with the top portion of the image adjacent a long edge of the sheet, feeding the sheets LEF, with the image alignment transverse to the direction of sheet feeding, results in pad style duplex copies.
If the copy sheets could be rotated, i.e., the lead edge of the sheet could be converted to the trail edge of the sheet, while maintaining the first side image in the same plane, in addition to the normal duplex inversion, book style copying could be accommodated in sheets having images oriented transverse to the direction of sheet travel. Arrangements for rotation of sheets themselves are known, such as, for example, Xerox Disclosure Journal, Copy Rotator/Inverter, Vol. 9, No. 5, Sept./Oct., 1984, pp. 323-324, by R. E. Shaeffer, which discloses apparatus to rotate a sheet along a paper path by 180.degree. in order to provide correct duplex style copying. Such arrangements are problematic since they require handling each sheet in a copy set, increasing the probability of a jam, damage to the copy, misregistration, etc. Additionally, such an arrangement requires a long flat paper path, which may not be available in a small or compactly arranged copier.